One shot bookbinding, which is also known in the trade as perfect binding, is the most common method by which books are bound. Using this method, the sheets or signatures which make up a book are collated or stacked and are then held in a clamp to form a book block. Adhesive is then applied to the backbone of the book block using, for example, a two or three wheel glue pot. A cover is then applied to the backbone of the book block before the adhesive is set. The backbone of the book block may be roughed or notched prior to adhesive application but this is not a uniform practice.
Two shot bookbinding is also commonly used to bind books. Using this method, the book block is initially bound using a primer adhesive. The primer is typically a water based system, but may also be a hot melt adhesive. Due to the slow drying times of water based systems, the book backbone may be passed over burners or heaters to decrease the drying time. A second adhesive known as a covering adhesive or second shot, which is usually a hot melt adhesive, is then applied using a two or three wheel glue applicator, to the book backbone. The bookbinding process is then completed using the application of capping paper, cheese cloth or crash, and kraft paper prior to application of the cover.
One shot and two shot bookbinding are used to bind a variety of things including, but not limited to, pocket books and paperback books, magazines, catalogues, telephone or other types of directories, manuals such as computer manuals, and text books.
Hot melt adhesives are used widely for one shot and for two shot bookbinding because of the rapid rate of set that can be achieved, therefore increasing the number of books that can be bound in a set amount of time. The types of hot melt adhesives most often used are based on copolymers of ethylene and block copolymers. However, with the increasing use of recycled paper and highly coated, glossy substrates, such as for high fashion magazines, increased bonding performance is often required, and such hot melts sometimes lack the ability to bond these substrates.
The heat resistance of these hot melts often do not exceed 65.degree. C. Heat resistance refers to the temperature at which the adhesive will soften and fail, leading to separation of the cover from the backbone of the book, or separation of the sheets or the signatures from one another. Heat resistance is very important in the transportation of books in the summer months when temperatures in a transportation vehicle may be in excess of 70.degree. C.
Another disadvantage to the use of hot melts based on copolymers of ethylene or block copolymers is that ink solvent resistance is low. Solvents from the ink will migrate through the pages to the book back where the book cover prevents further migration. The concentration of solvent at this point leads to delamination of the book cover from the book back.
This has led to the use of hot melt polyurethanes or hot melt PURs. These adhesives are also known in the industry as hot melt moisture cures. PURs are high performance adhesives with excellent adhesion to difficult substrates such as recycled paper and highly coated, glossy substrates. PURs have excellent ink solvent resistance and excellent heat resistance which often exceeds 100.degree. C.
There are disadvantages to using PtJRs, however, such as very slow cure rates, and cost. Due to the slow cure rate, books may be shipped prior to cure. No mechanical testing may be performed on the book prior to cure. Quality control is therefore not performed, and there is no guarantee that the books will meet specification.
Binderies in which hot melts are currently being used cannot quickly change to the use of PURs because different application equipment is required. This in turn leads to high conversion costs if equipment must be purchased. PURs also have high raw material and manufacturing costs resulting in increased cost to the consumers.
For two shot bookbinding, polyurethane dispersions, which are water based systems, may be used as the primer.
Polyamides are commercially available from many sources including Henkel Kommanditgesellschaft auf Aktien located in Dusseldorf, Germany; Union Camp located in Jacksonville, Fla., and H.B. Fuller Co, a St. Paul, Minn. based company.
U.S. Pat. No. 4,419,494 to Puletti et al., issued Dec. 6, 1983, teaches the use of dimeric fatty acid based polyamides in combination with A- B-A block copolymers. The tensile strength of these products are substantially lower than those of the present invention as they are less than about 100 psi at 100% elongation at 21.degree. C. This patent does not disclose the use of polyamides for bookbinding applications.
European Pat. No. 633,919 to Heucher et al., issued Oct. 14, 1993, discloses a dimer fatty acid based polyamide used in combination with ethylene vinyl acetate or ethylene methacrylate copolymers and styrene-ethylene-butene block copolymers and hydroabietyl alcohol or polybutene. This is distinguished from the present invention in that it requires the use of a copolymer of polyethylene and block copolymer and a plasticizer all in combination with the polyamide. The resultant properties of these adhesives are not the same as those required for bookbinding applications. This patent discloses how to use these adhesives for bonding polyethylene, PVC, and metal but does not teach how to use them for bookbinding applications. These products are therefore useful for the limited purpose of bonding these difficult materials.
U.S. Pat. No. 4,791,164 to Wichelhaus et al. issued Dec. 13, 1988, describes a compatible mixture of a terpolymer based on ethylene and a polyamide. However, this patent, as does European Pat. No. 633,919, teaches the use of these products for the limited purpose of bonding metals and polar and apolar plastics such as polypropylene or polyethylene. It does not teach how to use polyamide blends for use in bookbinding applications.
U.S. Pat. No. 4,018,733 to Lopez et al., issued Apr. 19, 1977, discloses blending polyamides with acidic ethylene polymers and tackifying agents. It again teaches how to use these blends for the limited purpose of bonding plastics such as polyethylene and metals such as lead. It does not disclose how to use these blends for bookbinding applications.
U.S. Pat. No. 5,026,756 issued Jun. 25, 1991 and U.S. Pat. No. 5,091,454 issued Feb. 25, 1992 to Arendt teach the use of 1,4-cyclohexane dimethanol dibenzoate in combination polyamides but do not teach how to use this combination for bookbinding applications.
U.S. Pat. No. 4,409,373 to Wiemers et al. issued Oct. 11, 1983, and U.S. Pat. No. 4,777,238 issued Oct. 11, 1988 and U.S. Pat No. 4,914,162 issued Apr. 3, 1990 to Leoni et al. disclose how to make polyamides but do not disclose a use for bookbinding.
U.S. Pat. No. 4,728,688 to Tizzard et al., issued Mar. 1, 1988, teaches the use of a water based primer for the first adhesive, and segmented EVA copolymer or a segmented monoalkene-vinyl acetate copolymer and a tackifying resin as the second adhesive for two shot bookbinding but does not teach the use of polyamide blends for two shot bookbinding.
Typical hotmelt polyamide adhesives have not been used as bookbinding adhesives due to poor heat stability. Typically, hot melt polyamides have to be applied above 200.degree. C. because of their high melt points and high viscosities. These very high application temperatures cause the polyamides to degrade and prevents their use in bookbinding applications. The degradation of polyamides results in char. Char causes uneven application of the hot melt polyamide to the book which results in poor adhesion at certain points. Also, hot melt polyamide adhesives typically have low elongation values which prevent good lay flat characteristics for books. Lay flat refers to the ability of books to remain open when no pressure is applied such as from a hand.
Surprisingly, the current inventors have found that by blending hot melt polyamides, or by blending other polymers, tackifiers, or plasticizers with hot melt polyamides, the properties required for bookbinding applications can be achieved. These blends lead to better specific adhesion which is required for UV coated paper, glossy coated paper, or recycled paper. By blending polyamides with other materials, lower viscosities can be obtained requiring a lower temperature of application which improves pot stability. The problem with degradation of polyamides therefore is eliminated. Higher elongation values are obtained which is required for good lay flat. Hot melt polyamide blends have a fast set time which allows for quality control testing prior to shipment, assuring that books are meeting required specifications. The heat resistance of hot melt polyamide blends may exceed 95.degree. C. which is much higher than that of hot melts based on copolymers of polyethylene or hot melts based on block copolymers.
Standard hot melt application equipment may be used to apply hot melt polyamide blends so the conversion costs realized with the use of PURs is not a factor.